1 This International Standard establishes a system of designation for filament yarns of carbon fibre which may be used as the basis for specifications.2 This designation system is applicable to filament yams used for the reinforcement of polymer composites.It does not apply to discontinuous fibre products pyrolized in the form of staple yarns, woven fabrics, braids, knits, mats, etc.3 The types of filament yarns are differentiated from each other by a classification system based on appropriate levels of the designatory properties:a) tensile modulus of elasticity;b) tensile strength;c) linear density.4 It is not intended to imply that materials having the same designation give the same performance. This International Standard does not provide engineering data, performance data or data on processing conditions wNch may be required to specify a material for a particular application and/or method of processing.5 In order to specify a filament yarn for a particular application or to ensure reproducible processing, additional requirements may be given in data block 3 (see clause 3).